1. Field of the Invention
The present invention is directed to a removable rivet having a preformed head located at at least one end of the shank of the rivet.
2. Discussion of the Background
Rivets, whether blind (i.e. settable by access to one side only of the workpieces) or non-blind (i.e. settable by access to both sides of the workpieces) are set or installed by being permanently deformed, and are intended to form permanent joints. They are not intended to be removed. In this context, the term "rivet" is used to designate any such fastener which is not intended to be readily removable, and may include types of fastener outside of those which are commonly known as "rivets" in the fastener trade and in engineering practice.
However, it sometimes happens that the workpieces must be later separated, e.g. for repair, or unforeseen servicing, of the structure of which they form part. Consequently it is then necessary to remove one or more rivets. Since in most cases it will be necessary to remake the disassembled joint, it will be necessary on reassembly to install a replacement rivet in the same overlying holes in the workpieces. Accordingly removal of the rivet must not damage or distort the hole or its surrounding workpieces.
It is usually found that it is sufficient to separate the head of the rivet from its shank. Since there is relatively little engagement between the shank of a set rivet and the adjacent wall of the workpiece hole, the shank and the integral head at its other end are then easily removed.
U.S. Pat. No. 4,451,761 discloses a rivet with an annular groove at the junction of the head and shank, for the purpose of weakening the junction so that the rivet head can be torn off the shank by gripping the head and pulling manually with a pair of pliers. This solution would be applicable where the material of the shank and head is relatively soft and weak (e.g. alluminium). However it would not be applicable to rivets made of stronger material (e.g. steel).
Since rivets are commonly circular in cross-section, comprising a cylindrical shank, one convenient way of detaching the head from the shank would be by drilling out. That is to say, a drill having a diameter the same as, or slightly larger than, the diameter of the rivet shank, is applied to the head co-axially with the rivet shank, so that it drills through the head until it meets the adjacent end of the rivet shank. If the drill is positioned accurately, little or no material remains connecting the head and shank, and the two are easily separated. However, if the drill is not accurately located co-axially with the shank, it will damage the workpiece. Since the drill must reach the circle at which the head and shank mutually abut the nearer end of the workpiece hole, damage to the workpiece around the hole is very likely. Furthermore, the rivet may spin in the hole before separation, ,due to engagement with the rotating drill, thereby frustrating the drilling operation and also possibly damaging the workpiece.